A mobile device, such as a smartphone or another portable computing apparatus, may run a search engine that receives queries, for example, from one or more users and returns query results responsive to the queries. For example, the search engine run by the mobile device can identify documents responsive to a query, generate query results with information about the documents, and provide the query results in response to the query. Other types of query results, for example, direct answers to questions posed by the user, or a summary of information responsive to the user's query, can also be provided. The usefulness of a search engine for a mobile device can depend on its ability to provide satisfactory query results.